Mileage Plus members who are planning on traveling to or through London Heathrow Airport before Aug. 31 will have a complimentary upgrade to Business class awaiting them.

Members who purchase two or more qualifying United Economy full-fare tickets in Y or B booking classes on the same flight to London will receive an automatic upgrade to United Business class. In addition to the free upgrades, members will earn 150 percent elite-qualifying miles and 125 percent of miles flown, based on upgraded class of service.

The free upgrade offer is only available to Mileage Plus members residing in the United States, Canada, Puerto Rico and the U.S. Virgin Islands. To receive a complimentary upgrade, members must book travel by calling (800) JET-AWAY and mention promotion code MLYBU1 and profile name S*PMO/London MLYBU1.

For more information, visit http://www.united.com/londonupgrade